The present invention generally relates to endoprosthesis devices, to procedures for making them, and to the use thereof. More particularly, the invention relates to endoprostheses having a generally tubular shape and a generally helical construction that includes end turnings which are welded to adjacent turnings of the structure. Preferably, the welding procedure is carried out in an environment that promotes the formation of welds which are essentially crack-free and provide a welded attachment that is less susceptible to possible failure during operation of the endoprosthesis.
Endoprostheses incorporating the invention are radially expandable between a generally unexpanded insertion circumference and an expanded implantation circumference which is greater than the unexpanded insertion circumference. Included are a plurality of generally circumferential sections of the substantially helically shaped endoprosthesis, and at least some of these sections include one or more expandable segments that are bendable members which are generally collapsed when the endoprosthesis is in its generally expanded insertion orientation and which are generally opened when the endoprosthesis is in its expanded implantation orientation.
In general, endoprostheses are known for treating stenoses, stricture, aneurysm conditions, and the like. Endoprosthesis devices of this type, which are at times referred to as stents, are typically placed or implanted by a mechanical transluminal procedure. Often, these devices are percutaneously implanted within the vascular system to reinforce collapsing, partially occluded, weakened, or abnormally dilated localized sections of a blood vessel or the like. Stents of this type can also be used in the urinary tract, the bile ducts, the intestinal tract and the like. When endoprostheses or stents are used to treat a stenosis condition, typically this is done in association with a dilation element such as an angioplasty balloon. In this instance, the dilation element or balloon device opens the constriction, and the stent or the like is positioned thereat in order to prevent or at least substantially slow re-formation of the stenosis.
Various currently known stent products have structures that are essentially coiled springs. When this type of spring stent is tightly coiled, its diameter is reduced for insertion through a blood vessel or the like. When the coil is sprung or coiled more loosely, the stent assumes its expanded, implantation configuration. Maass et al U.S. Pat. No. 4,553,545 is illustrative of this type of coiled spring stent or endoprosthesis. Multi-helix or braided stents are also known. Stents of this general type suffer from poor maneuverability, and they are relatively thick walled and three-dimensional. They are also difficult to remove once implanted, and they may exhibit numerous exposed, relatively sharp or jagged ends. Palmaz U.S. Pat. No. 4,733,665 is representative of an expandable stent of this general type. Gianturco U.S. Pat. No. 4,580,568 illustrates a percutaneous endovascular stent formed of stainless steel wire that is arranged in a closed zig-zag pattern somewhat in the nature of a bookbinder spring. Such a structure is somewhat unsymmetrical, and it may be subject to reocclusion due to the very large open space that is typically present between the wires of this t e of device. Another type of stent is known as a Schatz stent, and it includes a hypodermic tube with longitudinal slots etched into its body. While such a device has a high ratio of unexpanded to expanded diameter, it is a comparatively rigid, sharp-edged device which is difficult to maneuver through a tortuous path and is not easily remove in a transluminal manner.
Wiktor U.S. Pat. No. 4,886,062 illustrates a generally helical endoprosthesis having a zig-zag pattern that can be expanded by an angioplasty balloon, the general helix shape having two free ends that present loose portions of the stent. In at least one other approach, means are provided for engaging free ends of a generally helically shaped endoprosthesis in order to avoid the presentation of loose ends.
With many of these currently developed or proposed stent structures, the axial length of the stent decreases as the circumference of the stent increases, which can be a disadvantage. For example, any such length reduction must be taken into consideration in selecting proper stent sizing for a particular implantation procedure. Also, this attribute of many prior stents requires the passage through the blood vessel or the like of a stent which is longer than the length actually needed for the implantation procedure being performed. This is a particularly difficult problem for procedures in which the stent must be passed through a pathway having twists or turns, especially for a stent structure that is not easily bendable. Other stents have design features which can decrease patency or which do not secure components together in a manner that reduces the possibility of cracking at securement locations.
The present invention avoids the various deficiencies of these types of prior art structures and provides important and advantageous features of endoprostheses or stents and the use thereof, including the following attributes which are believed to be important and advantageous for stents.
One important desirable attribute of the present stent is that it is radially compressible and expandable in a controllable manner. It provides a cylindrical supporting surface that remains free of portions which either project into the passageway defined within the cylinder or form an outward projection that could damage a vessel wall. The stent can easily pass through a blood vessel or the like when collapsed and expand to its implanted size in a substantially predictable manner after the stenosis, aneurysm or the like has been reached to provide a stent exhibiting excellent patency. It is constructed to minimize any possibility of damage to the vessel within which it is deployed.
Another desirable feature is that the stent is generally flexible throughout its length so that it is easily maneuverable through bends, branches and curves of the blood vessel or the like. The stent or endoprosthesis has a substantial amount of open space so as to allow for endothelialization along its length to minimize interference with collateral blood vessels and the like. The stent or endoprosthesis can be lodged securely into place at the desired location, while still being removable through a transluminal percutaneous procedure, should removal be needed.
In summary, the endoprosthesis of this invention includes a plurality of generally circumferential sections that are generally adjacent to one other along their respective opposing generally circumferential edges. At least one of these sections has an expandable segment that imparts radial expandability to the section. The expandable segment is an elbow-like member which is bendable between a generally collapsed or closed orientation and a generally opened orientation and is capable of assuming bending orientations between one that is fully closed and one that is fully opened. By this structure, the endoprosthesis or stent has an unexpanded insertion circumference and an expanded implantation circumference which is greater than the insertion circumference. The stent is made by a procedure that includes welding free ends to attach same to another portion of the stent, this preferably being carried out in a manner which minimizes cracking and possible subsequent welded attachment, while providing a stent that can be easily reduced in radial size and transluminally explanted if necessary.
It is a general object of the present invention to provide an improved radially expandable, axially extending endoprosthesis of enhanced patency and durability.
Another object of the present invention is to provide an improved endoprosthesis or stent that can be constructed to have very well-controlled radial expansion capabilities.
Another object of this invention is to provide an improved radially expandable axially extending endoprosthesis that is extremely maneuverable and capable of moving through a tortuous path.
Another object of the present invention is to provide an improved radially expandable axially extending endoprosthesis that can, if desired, be transluminally explanted by means of, for example, a snare lead or catheter device.
Another object of the present invention is to provide an improved radially expandable axially extending endoprosthesis which has no unattached free ends.
Another object of the present invention is to provide an improved axially extending endoprosthesis and procedure for securing otherwise free ends thereof to generally adjacent portions of the endoprosthesis.
Another object of this invention is to provide an improved procedure for making an axially extending and/or generally tubular endoprosthesis that is radially expandable and that has portions secured together.
Another object of the present invention is to provide an improved procedure and stent made thereby by which securement of an otherwise free end of a stent to another portion of the stent is carried out in a manner to minimize or virtually eliminate cracking at the attachment location.
Another object of the present invention is to provide an improved radially expandable endoprosthesis that substantially avoids the presentation of any unattached edges or ends which might damage a medical device balloon or otherwise present portions which project beyond the generally cylindrical sheath structure of the endoprosthesis.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.